How much gold is there in our sun?

  • XKCD 1944 claims that there is "more gold in the sun than water in the oceans". Is this really true?



    The end of the rainbow


    Who here would dare contradict xkcd.com ? :-)

    Alt text for people that don't want to click through to XKCD: _"The retina is the exposed surface of the brain, so if you think about a pot of gold while looking at a rainbow, then there's one at BOTH ends."_

    @StephenG Much as I hate to contradict XKCD, that's not how rainbows work. You don't get a partial rainbow if there's simply a cloud in the right position. It has to be raindrops.

  • user1569

    user1569 Correct answer

    4 years ago

    The mass of the sun is 1.989 × 1030 kg.



    Abundance in the Sun of the elements gives a percentage 1 × 10-7 % for gold *, so that leaves you with a mass of 1.989 × 1021 kg of gold.



    HowStuffWorks states that there is 1.26 × 1021 kg water on Earth, of which 98% is in the oceans, i.e. 1.235 × 1021 kg.



    This would mean the XKCD statement is true: there is 1.6 times as much gold in the sun as there is water in the oceans.



    * They cite WolframAlpha as their source. Executing SolarAbundance "Gold" there confirms this (mass) percentage.


    There are at least two problems with that calculation: (1) The source for abundance doesn't say whether the percentage is of mass or of number of atoms; (2) if is it percentage of mass, 1 × 10-7 % means somewhere between 0.5 × 10-7 % and 1.5 × 10-7 %, so the proportion could be as low as 0.8, which is less than 1.

    How did that gold get there? I am under the impression that, as a main sequence star, the sun cannot create its own gold through element synthesis. So I am guessing that the gold in the sun was present when the sun first started burning, and I guess it must come from older generation supernovae?

    @ChocolateAndCheese Correct, virtually all of the elements heavier than Helium in the Sun (and the rest of the solar system) are the remains of older stars.

    @ Peter Taylor, similarly, the XKCD cartoon doesn't state whether it is more by mass or more by number of atoms/molecules.

    @Octopus or by volume. 2 lbs of gold is quite a bit smaller than 1 lb of sea-water.

    @ChocolateAndCheese yes -- the same way it got in the earth :)

    What is the uncertainty of this abundance-of-gold-in-the-Sun estimate? Without uncertainty estimates, the question which one is more cannot be answered.

    "1 × 10-7 %" sound really weird. Would 1 part per billion be better, or do we run into American versus British English problems?

    @gerrit That is always the case. Mathematically speaking, since the abundance is given with only one significant digit, the answer should be too. But we are talking about a comic here, not a scientific publication.

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Content dated before 7/24/2021 11:53 AM

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